Existing light emitting diodes (“LEDs”) can emit light in the ultraviolet (“UV”), visible or infrared (“IR”) wavelength range. These LEDs generally have narrow emission spectrum (approximately +/−10 nm). As an example, a blue InGaN LED may generate light with wavelength of 470 nm+/−10 nm. As another example, a green InGaN LED may generate light with wavelength of 510 nm+/−10 nm. As another example, a red AlInGaP LED may generate light with wavelength of 630 nm +/−10 nm.
However, in some applications, it is desirable to use LEDs that can generate broader emission spectrums to produce desired color light, such as white light. Due to the narrow-band emission characteristics, these monochromatic LEDs cannot be directly used to produce broad-spectrum color light. Rather, the output light of a monochromatic LED must be mixed with other light of one or more different wavelengths to produce broad-spectrum color light. This can be achieved by introducing one or more fluorescent materials into the encapsulant of a monochromatic LED to convert some of the original light into longer wavelength light through fluorescence. Such LEDs will be referred to herein as fluorescent LEDs. The combination of original light and converted light produces broad-spectrum color light, which can be emitted from the fluorescent LED as output light. The most common fluorescent materials used to create fluorescent LEDs that produce broad-spectrum color light are fluorescent particles made of phosphors, such as Garnet-based phosphors, Silicate-based phosphors, Orthosilicate-based phosphors, Sulfide-based phosphors, Thiogallate-based phosphors and Nitride-based phosphors. These phosphor particles are typically mixed with the transparent material used to form the encapsulants of fluorescent LEDs so that original light emitted from the semiconductor die of a fluorescent LED can be converted within the encapsulant of the fluorescent LED to produce the desired output light.
A concern with conventional fluorescent LEDs is that a significant amount of light generated from a semiconductor die is lost due to reflection at the interface between the semiconductor die and the fluorescent encapsulant, which reduces the overall LED light output. This reflection at the die/encapsulant interface is partly due to mismatch of indexes of refraction at the interface.
In view of this concern, there is a need for a device and method for emitting light with increased light extraction from a light source, such as an LED semiconductor die.